Method Of Operating Arc Lamps



No. 447,920. Patented Mar. 10, 1891.

TH: wams Farias co., mormumo., wnsnmsrou, u. c.

UNITED STATES PATENT OEEICE.

NIKOLA TESLA, OF NEW YORK, N. Y.

METHOD OF OPERATING ARC LAMPS.

SPECIFICATION forming part Of Letters Patent No. 447,920, dated Marchl0, 1891.

Application filed October l, 1890.

To all whom, it may concern:

Be it known that I, NIKOLA TEsLA, a subject of the Emperor ofAustria-Hungary, residing at New York, in the county and State of NewYork, have invented certain new and useful Improvements in Methods ofOperating Arc Lamps, ot' which the following is a speciiication.

This invention consists in an improved method of operating electric-arclamps which are supplied with alternating or pulsating currents.

It has now become a common practice to run are lamps by alternating orpulsating as distinguished from continuous currents; but an objection tosuch systems exists in the fact that the arcs emit a pronounced sound,varying with the rate of the alternations or pulsations of current, butunder anycircumstances constituting an objectionable and disagreeablefeature, for which heretofore no effective remedy has been found orproposed. This noise is probably due to the rapidly altern ating heatingand cooling and consequent expansion and contraction of the gaseousmatter forming the are which corresponds with the periods or impulses ofthe current, for I have succeeded in abating it and producing quiet andsmoothly-acting lamps by increasing, per unit of time, the number ofalternations or pulsations of the current producing the arc to such anextent that the rate of the vibrations or changes in the arc producingthe noise approximately equals or exceeds that which is generallyregarded as the limit of audition. For example, I may use a generatorwhich produces ten thousand or more alternations of current per second.In such a case the periodical heating and cooling of the are would occurwith such rapidity as to produce little or no perceptible effect uponthe ear.

There are a number ot' ways in which the current may be varied at a rateexceeding the limit of audition, but probably the most practicable knownto me at present is by the use of an alternating-current generator witha large number of poles, and specially const rueted for the purpose.Such a generator, for the purpose of the illustration of this case, Ihave shown in the accompanying drawings.

Figure l is a view of the generator in side elevation. Fig.Y 2 is avertical cross-section Serial No. 366,734. (No model.)

ot' the same with a diagram ot' the circuit-connections. Fig. 3 is anenlarged view, in side elevation, of a part ot the machine. Fig. a is anenlarged sectional detail of the armature and field. Fig. 5 is a detailsection of the ieldmagnets exhibiting the plan of winding.

A is an annular magnetic frame supported by the cross-bars or bracketsB, provided with feet O, upon which the machine rests. The interior otthe annulus A is provided with a large number of projectionsorpole-pieces I). These may be formed or applied in a variety ofways-as, for example, by milling transverse grooves E.

Owing to the very large number and small size of the poles and thespaces between them, I apply the exciting or held coils by winding aninsulated conductor F zigzag through the grooves, as shown in Fig. 5,carrying said wire around the annulus to form as many layers as isdesired. In this way the pole-pieces D will be energized withalternately opposite polarity around the entire ring.

For the armature I employ a spider or circular frame G on adriving-shattll, mounted in bearings in the brackets B. This spidercarries a ring J, turned down, except at its edges, to form atrough-like receptacle for a mass of tine annealed iron wires K, whichare wound in the groove to form the core proper for the armature-coils.Pins L are set in the sides of the ringJ and the coils Mare wound overthe periphery of the armature-structure and around the pins. The coils Mare connected together in series, and these terminals N carried throughthe hollow shaft II to con* tact-rings P P, from whence the currents aretaken ott by brushes O. In this way a machine with a very large numberof poles may be constructed. It is easy, for instance, to obtain in thismanner three hundred and seventy-tive to tour hundred poles in a machinethat may be safely driven at a speed of iifteen hundred or sixteenhundred revolutions per minute, which will produce ten thousand oreleven thousand alter-nations of current per second. Arc lamps R R areshown in diagram as connected up in series with the machine in Fig. 2.It sucha current be applied to running are lamps, the sound produced byor in the arc becomes practically inaudible, for byincreasing the rateofh-ange IOC in the current, and consequently the number of vibrationsper unit of time of the gaseous material of the arc up to or beyond tenthousand or eleven thousand per second, or to what is regarded as thelimit of audition, the sound due to such vibrations will not be audible.The exact number of changes or undulations necessary to produce thisresult will vary somewhat according to the size of the arc-that is tosay, the smaller the are the greater the number of changes that will berequired to render it inaudible Within certain limits. Of course, as therate ot' alternations or undulations for a given size of arc becomesvery high the sound produced is less perceptible, and hence for somepurposes the actual limit of audition may only be approached, providedthe sound be rendered practically inaudible.

Another advantage gained by increasing as above set forth the number ofalternations is that the arc acts more like that produced by acontinuous current, in that it is more persistent, owing to the factthat the time interval between undulations is so small that the gaseousmatter cannot cool down so far as to increase very considerablyinresistance.

I claim- The method of abating or rendering inau-

